composite solid tube

[Maciej]

Hi, I am thinking which material should I use for a plug to make composite tube diam 185mm.

It will be for bow thruster so diameter and shape has to be exact.

Generally it could be steel pipe but I am not sure if it is the best option. If you guys have any experience I would appreciate any ideas.

[gonzo]

Any material works. You can use PVC

[Maciej]

Thanks Gonzo, did you make any tube before? I know I can use any material but I am afraid about sufficient material for shape , easy to unmould. The best would be this one that can be slided off easiliy.

There are also polyamide tubes (thin plastic film that is blown to shape of tube) does anybody had any experience with this staff?

[Herman]

Easiest is a PVC or an Aluminium tube. If possible, apply teflon coated glass fabric to the tube (the version without texture). If not, make sure you apply a very good mold release.

Then apply your glass with epoxy resin. (polyester shrinks too much, will make your tube get stuck around the mould. If you want to use polyester, please check my second option)

After laying the glass, heat the tube gently by putting it in an oven, at 40-50 degrees C. This will make the tube expand. When the resin is cured, let it cool, and the tube will pop right off.

Another possibility:
cut a slot lengthwise in the tube, and hammer in a piece of wood. Put some tape over the seam. Now laminate the tube. After cure, remove the wood, and the PVC tube will pop back in its original shape, and can be removed.

[Maciej]

Thanks Herman, your information is what i looked for. I am afraid about shrinkage of resin (6-8%) but also epoxy could be difficult for polyester hulls. The best option for me is the second option. many thanks.

I have an offer for polyamide tubing (thin foil, blown to shape) , that is also solution, the only thing i am afraid is shape along the full length.

Thanks once again guys.

[Herman]

Nylon film is not stable enough. I would look for another (thick) plastic tube.

Steel pipe works great. The guys here use bear grease, believe it or not (I use mold release wax AND PVA). Poly works fine - When it is cured, throw it in a snow bank overnight, wrap it with towels in the morning, pour hot water on the exterior and the pipe will fall out with little coaxing. Epoxy can be tenacious on aluminum if a spot isn't prepped right. Like Herman said is ideal but hard to get a piece that big in an oven sometimes.

[Maciej]

ok, i will find steel or PVC tube with proper diameter then. thanks to all of you.

[Herman]

An oven can really be a make-shift thing. A couple of insulation plates, and a small heater (heatgun) can be enough.

Good point. I hope he gets that.

[Maciej]

now i need to find 185mm tube, it is not easy...